Internal rotor



Aug. 28, 1928.

M. F. .HlLL

INTERNAL ROTOR Filed Jan. 14, 1928 INVENTOR. khbnm flU L Patented Aug. 28,1928

1,682,563 UNITED STATES PATENT'OFFICE.

MYBON F. KILL, F YORK, N. Y.

' ETERNAL ROTOR.

Original application filed. November 5, 1921, Serial No. 513,075. Divided and this application filed January 14, 1928. Serial No. 246,894.

This case is a division of my application #513,Q75, filed November 5,1921; which, as to the invention herein contained, was a con tinuation of my'application #477,494, filed June 14, 1921'.

My invention relates to internal rotors; that is, two gears, one within another, having tooth divisions, one having one less tooth division than the other and the teeth of each continuously sliding in contact over the contour of the other.

In general, the method is put into effect, after selecting sizes of pitch circles proportional to the number of rotor teeth, and the size and form of a master tooth or tool form, by mounting the master tool upon means to revolve it around one base or pitch circle while it cuts a blank rotatin speed, properly proportional without variation to the numbers of teeth. This generates one rotor;

A mating tool having one tooth division or a convex tooth form, is then generated in the same way, and the same process applied to the other rotor; the mating tool during its cutting operation being rotated around the on a blank for the other or mating rotor, ro-

tating on its axis at proper relative speed.

The convex tooth curves of this mating rotor were assumed as the master form but the tooth spaces were not known and had to be thus generated. In other words the contours have -geometri cal outlines produced by three elements, namely two rolling circles and a master curve assisted by a fourth derivative element, a mating curve.

Let two circles be located upon, a plane, one within the other and tangent to it. Let their, diameters be in proportion to the numbers of tooth divisions selected for the two rotors which should differ by one. A master curve to represent the desired tooth'form of a rotor (either rotor) is selected to start the curve generation with and located upon the radius of the circle representing that, rotor 'whose tooth form is so selected. 7

If the master curve (or the mating curve) is located upon the radius of the .inner'circle it should have convexity upon its outer side about the cen ter of the other pitch circle, at a'relative element.

Appl ing this description now to the spe--; iciiic em odiment of my invention, the master curve selected is a smaller circle, or 'portion jofits periphery, representing the addendum center of the rotor already formed, so that it 1 follows the path of a tooth of that rotor and cutting'in each successive position a contour motion.

and if located upon the radius of the outer circle it should have convexity upon its inner side. One circle is rolled with the other without slip at the point of tangency which results in steady angular motion of one with relation to the other determined by their "relative diameters or in the inverse ratio of the numbers of tooth divisions, and the curved form traced in all the successive positions which it assumes with relation to the other circle, and a curve then drawn along the crests. of the traced curves as a curve of envelopinent which is the contour that is sought for one rotor element. A portion of the con tour, which may be called the mating curve is theucarried by the radius of the other circle, as the rolling action is continued in the same way, and its form in every successive position with relation to the first circle is traced; and a curve of envelopment is drawn along the crests of the curves so traced. This latter curve isthe contour of the other rotor or convex crown of a tooth of the inner rotor.

It is located upon the radius of the inner rolling circle with the center of the are on or outside the periphery, depending upon its size other circle. This inner circle may rotate nine times while the outer circle rotates eight times or at speeds inversely proportional to the numbers of teeth selected. This relative speed not being-varied has a steady angular The contour or outline of the nine tooth rotor, the outer rotor,'is the curve of envelopment traced alongthe crests of these traced curves. 4

A portion of thisc'urve of envelopment,

The two circles, with the radius ,of the inner circle carrying this master curve, are then rolled, one with the other and the fposition of this are traced in each successive.

position which it assumes with relation to the i having a convex side toward the center of the rolling circle is then the mating curve. It comprises the entire convex portion of a tooth division. It is located upon the radius of the outer circle inits outlined or generated position and the two rolling circles again rolled in the same way and the mating curve D is traced in all its successive ositions with relation to the inner circle. I the outer cir cle rotates eight times the inner circle rotates nine times, thus rotating at speeds inversel proportional to the numbers of tooth divisions of the two rotors. A curve of envelopment is then drawn thru the crests of these traced curves which is the'contour or outline of the inner rotor element.

Such rotors cooperate in the manner specified.

A convenient method of laying out these curves is to mount the describing curv'e either the master curve or mating curve-upon an arm which is swung around the center of the circle to which it belongs and rotate a blank around the center of the other circle and trace upon the blank the describing curve in all the successive positions which it assumes, the arm and the blank rotating upon their centers at speeds inversely proportional tothe numbers of tooth divisions of the rotors.

Instead ofrolling both circles, one circle may remain stationary and the other rolled in or on it as the case may be, always main: taining the point of tangencywithout slip. Thisis equivalent to mounting the circles upon a plane rotating backward as fast as one of the circles rotates forward, thus neutralizing its motion. Nevertheless with relation to such a plane their speeds still vary in inverse ratio, or inversely proportional to thenumbers of tooth divisions of the rotor elements.

In the mechanical operation of making rotors, the two rolling circles mentioned are the base or pitch circles of the actual rotors which vary in diameter in proportion to the numbers of tooth divisions. The master curve selected is the form of a milling cutter dimensions.

having cutting teeth upon its outer diameter. The mating curve has the characteristic of the convex portion of the tooth of the outer rotor, and its generated position on the base circle.

The two base circles and the master milling cutter determine the contour of the outer rotor and therefore the mating curve. That is, the mating curve is determined by those three elements.

The mating curve may have a variety of- A-blank for the outer rotor is selected with a hole in it to clear the tooth positions, so that there is material from which to form the teeth.

It may bemounted in a machine in which the milling -cutter is carried upon a fix- -ed axis, which corresponds to holding the inner base circle in fixed position,v as above described, The mechanic is supplied with figures to shift the table vertically and horizontally between cuts so that with relation to the blank'the milling cutter follows the successive positions of a tooth of the inner rotor. When both circles rotate the axis of the milling cutter rotates around the pinion axis as the blank rotates around the other axis.

But when the inner circle is the pinion axis is also fixed and a. blank rotates on its axis and the axis of the blank rotates around the pinion axis. In'either case the resulgix' curve is the same as hereinbefore descri If the rotors are .of the size shown in the drawings, twenty successive cuts from the to of a tooth to the bottom of the next'toot space, repeated for all the other teeth and tooth spaces; and twenty cuts from this bottomposition of a tooth space to the to of the next tooth similarly repeated will orm the'contour of the outer rotor. The surfaces have minute serrations which are removed by wearing the rotor into its mate.

The mating rotor, the pinion, is then to be formed. A shaping cutter or mating tool is then made having the contour of the convex portion of the tooth form of the outer rotor and mounted in a so called shaper, and a blank slightly larger than the outside diameter of the pinion orinner rotor is mounted on the table of the shaper. The mechanic is suppliedwith figures for rotating the blank by means of an index, and figures for settin the table in a series of horizontal and vertica positions and in each' position the mating tool cuts the blank. Such positions are the positions of the tooth form of the outer rotor with rel'ation to the contour of the inner rotor.

Twenty such positions from the top of a tooth of the inner rotor to the bottom of the next tooth space and twenty more from that point to the to of the next tooth, repeated for all teeth an tooth spaces, provide the contour or outline of the inner rotor. This method corresponds to the geometrical description above noted in which the inner circle is held stationary and the outer circle rolled upon it without slip at the point of tangency. The

tables of the machine em loyed for generation as in a milling mac e or shaper are supplied with micrometer divisions on the screws that adjust them, so that accurate settings arepossible. A milling machine may be used for the master tool and a shaper for the mating tool.

It is apparent to amechanic that rotors so made fit so tightly. one within the other that rotation isdiflicult, and one rotor has been worn into the other by'an operation which may be called burnishing which wears off the minute serrations between the cuts so that the rotors work freely together and maintain the contacts between their contours inthe region of tangency of the base circles 'w'hich is usually (in gear parlance) termed Ffull mesh and in the r on opposite where the base circles are fa est' apart usually termed open mesh; which are utilized in fluid mechanisms to keep the pressure in one passagemayfrom leaking thru the teeth over into the other passageway. In both full -mesh and open mesh regions this contact is travelling and continuous during rotation so that as t e teeth shift in their relative posibase or pitch circle, when there are eight tooth .and the outer a radius of nine units.

tions with each other and the tooth spaces they do not recede from each other at points which would permit a substantial dissipation of pressure from a high pressure passageway over into a low contours with their steady angular velocities maintain fluid tightness in these regions so that high mechanical and volumetric efiiciencies are made possible.

, WVhatever the master curve, and whatever the contour system it creates, th1s contmuous travelling fluid tight relation both at full mesh and open mesh regions is maintained.

If the diameter of the milling cutter is f ths (of'any unit of measurement) its center should lie .023 more or less, outside of the divisions of the form shown on the inner rotor, and nine tooth divisions on the outer rotor. The base or pitch circles var as 8 to 9, the'inner circlehaving a radius 0 8 units, Their diameters being 16 and 18 units respectively, which is proportional to the numbers of tooth divisions'selected for the rotors. I

When one rotor is burnished into the other as described, it is apparent that a tooth of one rotor makes such close engagement with the contour of the tooth space of the other rotor inthe full mesh region that the travellingengagement substantially preventing leakage is realized, and in use there is always at least one point of contact or engagement of the nature specified between the rotor contours substantially preyenting leakage in this region.

If the master form or milling cutter represents the tooth of the outer rotor and the mating curve represents the tooth form of the inner rotor the inner rotor is of course generated first by the master form and then the mating tool may be also generated so that it has theform of a tooth of the inner rotor and this mating tool then generates the outer rotor by the same method above described.

The two rotors have teeth theoretically always in mesh except where a tooth of one rotor at full mesh leaves one tooth of the other, rot-or in passingto the next; tooth of that rotor. v e

Various tooth face and flank curves have been proposed in text books for the teeth of gears, one inside of the other. Theoretical limits of ratios of such gears'have been referred to including a difi'er'ence of one tooth. But with such a difl'erence, the gear teeth were truncated or shortened toavoid clash at open mesh and for manufacturing purposes. The tooth and tooth space relation at full mesh was missing because of this truncated form.

My mutually generative rotor forms provide pressure 'passageway. My

Inventors and patentees, from time to time, have claimed that their rotors had sliding contacts, but failed to show or describe any method to attain such a result, or to define curves that could have it.

In the drawings Fig. I illustrates a pair of rotors and the pathways of the teeth of one with relation to those of the other in the specific curve system illustrated in this figure.

Fig. II is a section of the rotors on line II-'-II, Fig. I.

Fig. III is a master toolof the form selected for this specific system.

Fig. IV is a mating tool for the same system.

variation of my method.

Fig. VI is a section of the rotors in Fig. V on 'line VI-VI.

Fig. VII is any form of master tool selected to start with, to generate one rotor with.-

Fig. VIII is a mating tool generated by the master tool in Fig. VII, for generating the other rotor with.

One specific form of my method of making rotor curves is as follows A'pinion gear or rotor 1, Fig. 1, is provided having teeth 2 and tooth spaces 3, centered upon an axis 4. It iseccentric'to and works inside of an annular gear or rotor 5 having I Fig. V illustrates alternative specific I The exception to this contact between a given pair of teeth is at full mesh shown at the top of Fi 1 where, in the particular curve sys tem shown, there is an almost instantaneous shift of the contact of a pinion tooth, from one annular gear tooth 6 to the next one 6*, at which time, with perfect curves, the inion toothbarely touches the annular toot 'space in passing. Such an annular tooth, onthe contrary,'takes;time to roll on a pinion tooth space as it crosses full mesh, passing from one pinion tooth to the next one.

A pinion tooth 2 travels over an} annular tooths division 6, 7 during one complete rotation about the pinion axis. These 5 cific tooth and tooth space relations in ig.

1 may be secured by providing the pinion teeth withconvex surfaces of substantially circular form.

. In designing rotors, the eccentric rotor axes are. of course, located with proper itch ciroles, upon which the gears are esigned,

touching at one point, as in ordinary ear design, and proportioned to the numbers of teeth selected. A milling cutter of an approved size is selected as a master tool to cut either rotor with.

In the particular curve system shown in Fig. I, the master tool milling cutter 2 (Fig. III) is adapted to cut the teeth 6 and tooth spaces 7 of the annular gear or rotor 5. The milling cutter is started rotating at cutting speed in the position of a tooth of the pinion'as indicated at 9 for example; an annular blank being provided having a hole indicated in broken lines 10. (Other places may be used for starting the milling operation such, for example, as drilling a hole in some tooth position9 for example, where the mill may start cuttin the curve, and entering the mill into the ho-e.) The mill is then rotated at cutting speed upon its axis 2, in the position of the tooth of the pinion 1, with the axis .2 lying outside of the pinion base circle B, and revolved around the pinion axis 4 while ro tating the annular gear blank around its eecentric axis 8. If the speed of rotation of the mill around the pinion axis-the same as a pinion tooth around that axis-and of the gear blank around its axis vary for instance, as 9 to 8 respectively, the gearblank after nine-such rotations, will have nine teeth. A pinion having teeth with convex curves corresponding to the mill in form and size, will rotate harmoniously, with the annular gear so generated,in other words, at steady angular velocities-so far as the pinion convex tooth contours are concerned. The pinion tooth spaces remain to be determined.

The annular surface thus has enerated curves 6, 7 parallel to hypocyc oids, or rather to a variety of hypocycloids termed curtate trochoids, shown at 12, the axes of the pinion teeth and mill describing such curves. I term these trochoids circroids and the rotor contours in Figs. 1 phydocroids (see Kinematics of Gerotors by the ap licant on file in the U. S. Patent Oflice Li rary and elsewhere).

Any other plurality of teeth may be used provided the outeror annular gear or rotor has one more tooth division than the pinion.

Such a inion 1 should have the convex surfaces 0 its teeth 2 rovided with substantially the same radlus of curvature as that of the milling cutter.

The spaces between the pinion teeth may in turn be generated by means of a shaping tool having the form of a tooth space and tooth of the annular gear. A blank of tool steel may be substituted for the rotor blank 5 of the same size and shape and a single tooth 6 and tooth space 7, generated in the same way as the annular gear blank; and the mating tool 13-, Fig. IV, cut out of said blank as indicated at broken lines 14, Fi 1. The convex curve of such a mating tool is not circular when the master tool is circular. The tool 13, or'rather its convex portion, generates curves on the pinion that mate with the annular gear. This matin tool is rockcd, preferably between cuts, blank to assume the various positions that a tooth and tooth s ace of the annular gear. assume about a pinion. The convex portion of the mating tool, during this operation, generates a tooth space 3, and may in practice generate the whole pinion curve tho the convex pinion curves 2 were fixed by selecting the size of the mill and locating it at the point 2. The number of inion teeth, too, were assumed to start wit The axis 2 of the master milling cutter and of the-pinion tooth should be just enough outside of the pitch circle to form the good working curve above described.

And the mating cutter representing the curve of an annular tooth and tooth space if desired (mounted in a shaper machine for example) to shape the pinion teeth and tooth spaces, generates the pinion blank is caused to assume the positions relative to the mating cutter curve, that the corresponding portions of the pinion curve assume to the corresponding portions of the annular gear curve (or one of its teeth).

To sum up this mutually generative relatlon, the teeth and tooth spaces of either gear or rotor may be generated from the form of teeth of the other, and tooth spaces (and a out the pinion whole contour) of the other gear or rotor may be generated from the form of the teeth of the first gear or rotor to be generated.

Variations of my method, lying within its scope, are possible. Instead of starting with a circular master tool form representing a tooth of the inner rotor, it may represent the form of an annular tooth division on the outer rotor as illustrated in Fig. V. Various master forms Fig. VI may be employed, such as circular ones or ovals of different forms including cycloids, either a simple cycloid or a trochoid or a curve paral el to a trochoid or other forms. In each case, except with simple cycloids, the distance of its axis 2 outside of the base circles A, B,-which distance is called the curtate additi0nhas to be determined. Experiment with difi'ere'nt distances soon indicates the bestcurtate addition, to produce contours with continuous sliding contact-sas above described.

Some slight degree of lost motion between a pinion and annular gear is desirable for free action; that is, portions of the courves which have no needed function-as at 14 on the pinion rotoror any part of it, and portions at 14' on the annular rotor, or such parts thereof as are not needed for continuous contact, depending on the application of my invention,-may be varied-that is cut intoif desired, so that, in assembly, one rotor may enter the other freely. Th1s cutting away lln connects the rotor spaces or chambers together on the non-driving side. .My gears may be mounted upon journals, having the usual lost motion in the journals to permit free rotation without injurious heat. When the gears are first assembled on such journals, the pinion teeth at first ride hard upon the annular teeth at open mesh until the teeth Wear free and until the gears bear upon their journals instead of upon each other. It the annular gear drives the pinion in the direction of the arrows, the teeth bear against each other from open mesh tofull mesh, as on the left side of Fig. 11

If the pinion gear drives the annular gear when travelling clockwise, they bear on each other on the right side of Fig. 1, from full ished.

mesh to open mesh.

Except forthe length ofa tooth division nearest full mesh the pressure is reduced between the teeth that bear against each other until it is substantially eliminated, and the teeth assume a pressureless sliding contactl that keeps them smooth "and brightly pol- This action may be termed burnishing.

The tooth division, indicated by a double headed arrow Fig. 1, at full mesh is the driving range; and if it wears, the sliding con tacts elsewhere are again subjected to pressure until they wear free again to new curves. By such an action the gears wear tight. vWhen subjected to heavyemergency loads, these additional gear tooth contacts provide reserve driving strength and load sustaining power, as Well as add to their durability. This action between the teeth that keeps themtight regardless of wear is of Vital importance in working on or by high pressure fluids. These various tooth contacts, when combined in pumps or engines with ports to match the tooth contact action, provide rotor chambers that open and close and are able to perform expans on and contraction pressure functions, such as pumping fluids, or acting as motors, particularly for gases, with high efficiency, both from a volumetric and power standpoint. r

In Fig. V, in which the master tool representsthe tooth of an annular rotor, the axis of themaster tool, Fig. III or Fig. VII, follows thee icircroid curves shown in broken lines 15, uring generation ofthe fcontour 17 of rotor 16. "The mating tool, Fig. VIII, thereupon represents a tooth "of the pinion gear and generates the curve .18 on the outer rotor. When the master tool, Fig. v11, is a simple cycloid, the cycloid is erected on the base circle of the rotor, of which it represents no a tooth" (see Kinematics supra). In such a case, the generated teeth ofthe inner rotor are simple epi'cycloids, and the-generated tooth spaces are simpleh pocycloidsand the enerated tooth spaces 0 the outer rotor are awn simple epicycloids, l

'Whatever the master tool curve, in either Fig. l or .V, the mating tool has a curve de termined by the master tool. And the curves of the two rotorsare determined by these tools. It therefore follows that all ,rotor curves are determined'by the master tool Without limiting my invention to specific dius of the base circle A may be .92 and of B 1.035. The curtate addition, the distance of the axis of a pinion tooth-or of themill may belocated .023, more or less, outside of the base circle A (or less or more) to cut the outer rotor from. andof the milling cutter 2 may be .2187. The axis of the tooth 2 and that of the milling cutter dcscribe a star shaped figure of the character shown. at 12 in cutting the curve (3. 7. l In this specification and in the claims I have made the statement or used the expression that the curves of envelopment upon or by which the contours of the rotors are formed are generated by the tooth form dur- The radius of a tooth 2 ing relative angular motions inversely proportional to the numbers of teeth. I mean to indicate by this expression that altho the the place where the teeth engage, they necessarily vary in relative angular displacement, moving as they do on difiercnt radii and one having one less tooth than the other. In the ratio of 8:9 for example, the larger rotor would not have completed its revolutionby 40 when the smaller had made a complete turn. Necessarily this makes the teeth of one slide on the teeth of the other; and it is one '95 two peripheries travel at the same speed at" of the main objects of my invention to so form the "curves of envelopment of the two sets of tooth divisions during the working range which may be either using or delivering power) that the contours shall continu and can be efliciently-lubricated to form a film which is not removed either by the contact oftl fe metal or. bv fluid pressure. Inpractice'jafterthe teeth have become burnished no substantial .-lubrication between them is required for-tightness.

These proportions-may vary of course. If alterations are made in the size of the master tool, it 'shape, the specific system of generalHi ously. maintain travelling contact due to the llb tion, or other factors, trial cuts indicate the correct curtate addition to secure the best curves.

While I have described certain specific forms and applications of-my invention, it is understood that its scope is not limited to them but embraces such rotor contours as may conform to the structure or utilize the method, or novel aspects of them, herein described.

What I claim is 1-- g 1. A rotary mechanical movement comprising two rotor members having internal and externalteeth respectively, one within, eccentric to, and having one less tooth division than the other, each tooth having a radial height from the hollow of a tooth space to the top of a tooth substantially equaLto twice said eccentricity and the faces and flanks of the teeth of each rotor having contours generated by the form of the other at steady angular velocity, to provide continuous sliding contacts between the teeth in the open mesh region and the full mesh region.

2. Rotors claimed in claim 1, havingsaid continuous contacts extending from open mesh to full mesh.

3. Rotors claimed in claim 1, having a substantially circular tooth form -on one rotor and a contour on the other rotor having a generative relation to said circular tooth form.

4. Rotors claimed in claim 1, having a substantially circular tooth form on the inner rotor and the outer rotor having its contour in generative relation to said tooth form.

5. Rotors claimed in claim" 1, having contours unnecessary for continuous contact cut away, to allow free entry of onewithin the other.

6. Rotors claimed in claim 1, having their contours burnished together to maintain continuous contact and, except for a driving range at full mesh, to eliminate substantial pressure. 1

Signed at New York, in the county of New York and State of New York, this 9th day of January, A. D. 1928.

MYRON F. HILL. 

